1. Field of the Invention
The present invention relates to a Media Access Control (MAC) apparatus and method in a Wireless Local Area Network (WLAN) device. More particularly, the present invention relates to a multi-channel MAC apparatus and method for a WLAN device with a single radio interface.
2. Description of the Related Art
The Institute for Electrical and Electronics Engineers (IEEE) 802.11 standard has provided the basic technology for interworking of WLAN devices. IEEE 802.11 has succeeded in implementing timely amendments to the specification (for example, 802.11a, 802.11g, 802.11e, 802.11i, and 802.11n) addressing the different needs that become evident with time.
The core of the WLAN standard is to address a link between an Access Point (AP) and its Stations (STAs). The well-known topology for networking between the AP and the STAs is a Basic Service Set (BSS), and a set of STAs is controlled by a single mediator AP. A system and an integrated Local Area Network (LAN), used for making connections between BSSs, are called a Distribution System (DS). These days, the DS is generally made into a wired DS. The main object of IEEE 802.11s is to specify a function of allowing APs to wirelessly communicate with each other, and to build up a Wireless Distribution System (WDS) in which 802.11s nodes can deliver traffics on behalf of each other.
FIG. 1 schematically illustrates WLAN network elements.
Referring to FIG. 1, unlike the STA of the BSS, the basic element of an IEEE 802.11s mesh network is a Mesh Point (MP) 100. MPs, like the routers in the wired network, deliver frames hop by hop on behalf of other MPs, and provide wireless links between APs, also known as Mesh Access Points (MAPs) 110. Because the wireless links do not require the wired infrastructure, the present invention aims at enabling establishment of such hard-to-control devices, and the establishment of the WLAN mesh network makes it possible to rapidly cover the broader service area.
Because MAC layer routing and a management framework for the mesh network are the core elements of the WLAN mesh network, the present invention focuses on the management of multi-channel MAC operations. Generally, a WLAN access control scheme defines a mechanism in which more than two WLAN devices can communicate with each other in one channel. A single radio interface-based multi-channel access scheme means an independent IEEE 802.11 wireless device. In this scheme, one wireless device supports multiple wireless bands. However, even though one wireless device supports only one band at a time, it is regarded as a single radio interface. This single radio interface is based on an access scheme that uses one channel. This channel, which is commonly used by all devices, is called a common channel.
When the common channel switches to another channel for a multi-channel operation of MPs with a single interface, the state of the common channel is no longer sensed. That is, the MP cannot communicate with an arbitrary MP on the common channel. Even though a transmitting MP selects a data channel used for data transmission by exchanging Request to Switch (RTX) and Clear to Switch (CTX) frames with a receiving MP on the common channel, the transmitting MP cannot hear the RTX and CTX frames on another channel. In addition, because the RTX and CTX frames were designed to address the hidden node problem, the MP may break the ongoing data transmission after the channel switching.